The present invention relates to accelerometers in general and particularly to a crystal-based three axis accelerometer in a unitary package with the capability of varying sensor axis sensitivity in any given direction.
Navigational instrumentation using accelerometers is used in many different environments. For example, down-hole oil exploration tools typically employ three independent single axis sensors for determining acceleration. The single axis sensors, however, disadvantageously occupy substantial space in the exploration tool. Further, most current single axis sensors are force-balanced servo accelerometers using a magnetically restored proof mass and therefore produce a magnetic influence on their surroundings. The inertial navigational instrumentation, however, also includes magnetometers. The potential interaction between the highly magnetic accelerometers and the magnetometers requires the accelerometers to be placed a minimum distance from the magnetometers. Further, quartz crystal-based resonators have previously been employed in sensors and have been proposed for use in tri-axis accelerometers. For example, see U.S. Pat. No. 6,826,960. The tri-axis accelerometer of that patent involves a statically determinant system that does not afford sensitivity or enable variable sensitivity in any one or more directions without having to modify the individual crystals size or shape. Accordingly, there is a need for an improved tri-axis accelerometer having variable axis sensitivity capability which can utilize one standard support system (i.e., a support crystal).